<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <!-- postion布局 -->
    <div class="bg"></div>
    <div class="abc"></div>
    <!-- <div class="def"></div> -->
    <div class="bg"></div>
    <style>
      .bg {
        width: 80px;
        height: 80px;
        background-color: green;
      }
      .abc {
        width: 80px;
        height: 80px;
        background-color: red;
        /* static 未激活状态*/
        /* relative absolute fixed 激活状态*/
    position: absolute;
    /* absolute找最近的激活了position父容器 
    进行计算定位 */
    top:100px;
    left:100px;
        /* position: relative;
        top: 20px;
        left: 20px;
        z-index: 13; */
      }
      .def {
        width: 80px;
        height: 80px;
        background-color: blue;
        position: relative;
        top: 20px;
        left: 40px;
        /* buttom right */
        z-index: 33;
      }
    </style>
  </body>
</html>
